package generics;//: generics/LinkedStack.java
// A stack implemented with an internal linked structure.

public class LinkedStack<T> {
  private static class Node<U> {
    U item;
    Node<U> next;

    Node() {
      item = null;
      next = null;
    }

    Node(U item, Node<U> next) {
      this.item = item;
      this.next = next;
    }

    boolean end() {
      return item == null && next == null;
    }
  }

  private Node<T> top = new Node<T>(); // End sentinel

  public void push(T item) {
    top = new Node<T>(item, top);
  }

  public T pop() {
    T result = top.item;
    if (!top.end())
      top = top.next;
    return result;
  }

  public static void main(String[] args) {
    LinkedStack<String> lss = new LinkedStack<String>();
    for (String s : "Phasers on stun!".split(" "))
      lss.push(s);
    String s;
    while ((s = lss.pop()) != null)
      System.out.println(s);
  }
} /* Output:
stun!
on
Phasers
*///:~
